Particulate matter detection sensor and control device of controlling the same

ABSTRACT

A particulate matter (PM) detection sensor is placed in an exhaust gas pipe of a diesel engine. The PM sensor element has a detection part composed of a pair of detection electrodes and a heater part. The detection electrodes and the heater part are stacked in the PM sensor element. A control circuit instructs a heater power supply to supply electric power to the heater part when the diesel engine is started to operate. The heater part heats the detection part at a predetermined temperature T 1  within a range of 600° C. to 900° C. for a predetermined period S 1  of time, for example, 650° C. for 20 seconds, in order to burn and completely eliminate particulate matter accumulated in the detection part. This control process avoids incorrect detection of the PM detection sensor. After this process, the control circuit executes usual control of the PM detection sensor.

CROSS-REFERENCE TO RELATED APPLICATION

This application is related to and claims priority from Japanese PatentApplication No. 2010-147862 filed on Jun. 29, 2010, the contents ofwhich are hereby incorporated by reference.

BACKGROUND OF THE INVENTION

1. Field of the invention

The present invention relates to particulate matter detection sensorsand control devices of controlling such a particulate matter detectionsensor, and more particularly, particulate matter detection sensors ofan electric-resistance type and control devices of detecting a quantityof particulate matter contained in target detection gas such as exhaustgas emitted from an internal combustion engine. Such a particulatematter detection sensor is placed in an exhaust gas pipe of an exhaustgas purifying system of the internal combustion engine and is applied todetecting defect of a diesel particulate filter which traps or trapsparticulate matters contained in the exhaust gas in order to purify theexhaust gas.

2. Description of the Related Art

In general, a diesel engine exhaust gas system of a diesel engine isequipped with a diesel particulate filter (DPF). The DPF is placed in anexhaust gas pipe of the diesel engine exhaust gas system. The DPF cantrap and eliminate conductive particulate matter PM from exhaust gasemitted from the diesel engine. The particulate matter PM containsenvironmental harmful matter, in particulate, soot and soluble organicfraction (SOF), etc. The DPF is made of porous ceramics with a high heatresistance. When exhaust gas passes in the exhaust gas pipe, cell wallshaving pores in the DPF trap particulate matter contained in the exhaustgas in order to purify the exhaust gas.

When a quantity of particulate matter PM trapped in the DPF exceeds apredetermined allowable quantity, clogged cell walls occur in the DPF,and a pressure loss of the DPF is thereby increased. The clogged cellwalls in the DPF allow the particulate matter contained in the exhaustgas to pass through the DPF without trapping the particulate matter.This prevents the exhaust gas from being purified. In order to avoidthis, it is required to execute the regeneration of the DPF everypredetermined period of time in order to recover the trapping functionof the DPF.

For example, it is possible to detect the time to execute theregeneration of the DPF by using a differential sensor, because thepressure difference of the differential sensor is increased when thequantity of trapped particulate matter in the DPF is increased. In theregeneration of the DPF, combustion exhaust gas at a high temperature isforcedly introduced into the inside of the DPF by using a heater orexecuting post-injection in order to burn and eliminate the trappedparticulate matter from the DPF.

On the other hand, there has been proposed a particulate matterdetection sensor capable of directly detecting particulate mattercontained in exhaust gas emitted from an internal combustion engine.Such a particulate matter detection sensor is placed at a downstreamside of the DPF in order to detect the quantity of particulate mattercontained in exhaust gas after passing through the DPF. For example, anon-board diagnosis device (OBD) monitors the operation condition of theDPF can use the detection result of a particulate matter detectionsensor in order to detect defect and damage to the DPF.

When such a particulate matter detection sensor is placed at theupstream side of the DPF, it is possible to detect the quantity ofparticulate matter contained in the exhaust gas which is introduced intothe DPF and to detect the optimum time to execute the regeneration ofthe DPF, instead of using the differential sensor.

For example, Japanese patent publication No. JP H02-44386 discloses asoot concentration sensor of an electric resistance type. In the sootconcentration sensor, a pair of conductive detection electrodes isformed on a front surface of an insulation substrate, and a heater isformed on the back surface or in the inside of the insulation substrate.This soot sensor uses conductive characteristics of soot. The sootsensor detects an electric resistance which is changed in accordancewith the change of the quantity of soot particles accumulated betweenthe detection electrodes. The detection electrodes form a detection partin the soot sensor. A heater part generates heat energy when receivingelectric power in order to heat the detection part at a temperaturewithin the range of 400° C. to 600° C., and detect the resistancebetween the detection electrodes. After detecting the resistance, theaccumulated particulate matter is burned in order to eliminate theparticulate matter from the soot sensor and regenerate it.

In addition, Japanese patent laid open publication No. 2009-144577discloses a device equipped with a particulate matter trap sensor inwhich a plurality of electrodes, which face to each other at apredetermined gap, is formed on an insulation material. The devicecalculates an index corresponding to the electric resistance valuebetween the detection electrodes, and judges occurrence of faulty in aparticulate filter when the detected index becomes smaller than apredetermined reference value. Further, the device resets the PM trapsensor every regular condition (every predetermined driving time,predetermined driving distance, and quantity of used fuel).

There are other conventional techniques for detecting particulate mattercontained in exhaust gas on the basis of detecting heat energy generatedby oxidizing particulate matter by using catalyst and a thermocouple,monitoring temperature and chemical seeds contained in exhaust gas byusing wavelength variable diode sensor. In particular, particulatematter detection sensors of an electric resistance type have a simpleconfiguration and can output a relatively stable output signal.

By the way, there is a possibility of being particulate matter emittedfrom a previous combustion of an internal combustion engine and trappedand remained in a detection part of a particulate matter detectionsensor when the engine is restarted.

The former conventional technique (Japanese patent publication No. JPH02-44386) previously described burns off remained particulate matterwhich is trapped and accumulated on the particulate matter detectionsensor by continuing heating after completion of the detection process.However, when the detection process is executed, the temperature of theparticulate matter detection sensor is within a range of 400° C. to 600°C., and this temperature is not always an adequate high temperaturecapable of completely eliminating remained particulate matter from theparticulate matter detection sensor. Still further, it is difficult toregenerate the particulate matter detection sensor unless an adequateperiod of time is elapsed.

Still further, the sensor disclosed in the latter conventional techniqueJapanese patent laid open publication No. 2009-144577 is burned everypredetermined period of time for a predetermined time in order to resetthe sensor. However, there is a possibility of generating the enginestop without resetting the sensor completely.

This often causes incorrect output of the sensor after the enginerestart because the characteristics of particulate matter trapped andremained in the detection part of the particulate matter detectionsensor is changed by the environment during the engine stop or when theengine restart. For example, the sensor often outputs an incorrectdetection signal during the engine stop and when the engine is restartedby adhering water and oil components remained in the exhaust gas pipe tothe particulate matter detection sensor and by evaporating soot organicfraction (SOF) contained in particulate matter remained in the exhaustgas pipe.

SUMMARY OF THE INVENTION

It is an object of the present invention to provide a particulate matterdetection sensor of an electric resistance type and a control device ofpreventing particulate matter accumulated in a detection part of theparticulate matter detection sensor from being remained, and furtherpreventing the detection accuracy of the particulate matter detectionsensor from being deteriorated and decreased. The particulate matterdetection sensor according to the present invention outputs a stable andcorrect detection signal with high accuracy.

To achieve the above purposes, the present invention provides a controldevice which controls the operation of a particulate matter detectionsensor. The particulate matter detection sensor is placed in an exhaustgas pipe of an internal combustion engine through which exhaust gasemitted from the internal combustion engine flows and is discharged tothe outside. The particulate matter detection sensor is equipped with aparticulate matter sensor element. The particulate matter sensor elementis comprised of an insulation substrate, a detection part and a heaterpart. The detection part in the particulate matter sensor element iscomprised of a pair of detection electrodes formed on a surface of theinsulation substrate. The heater part generates heat energy whenreceiving electric power in order to heat the detection part at apredetermined temperature for a predetermined period of time.

The control device has a control part. The control part receives adetection signal transferred from the particulate matter detectionsensor and detects an electrical resistance value between the pair ofthe detection electrodes in the detection part on the basis of thereceived detection signal, etc. In general, the electrical resistancevalue between the pair of the detection electrodes is changed inaccordance with a quantity of particulate matter accumulated in thedetection part. The control part supplies electric power to the heaterpart. For example, the control part instructs a heater power supply tosupply electric power to the heater part.

In particular, the control part is comprised of a combustion controlmeans and a usual control means. The combustion control means executescombustion control when the internal combustion engine starts tooperate. The combustion control is executed when the engine is startedor restarted. In the combustion control, the combustion control meanssupplies electric power to the heater part in order to maintain thedetection part of the particulate matter detection sensor at apredetermined temperature T1 for a predetermined period S1 of time inorder to burn the accumulated particulate matter and eliminate theaccumulated particulate matter from the detection part of theparticulate matter detection sensor. On the other hand, the usualcontrol means executes usual control after completion of the combustioncontrol previously described which is executed when the internalcombustion engine is started to operate. In the usual control, the usualcontrol means supplies electric power to the heater part in order tomaintain the detection part of the particulate matter sensor element inthe particulate matter detection sensor at a temperature T2 which isless than the predetermined temperature T1 in order to detectparticulate matter adhered to and accumulated in the detection part.

The combustion control means in the control circuit according to thepresent invention executes the combustion control every time when theinternal combustion engine is started (or restarted) to operate. In thecombustion control, the combustion control means supplies electric powerto the heater part in order to execute the combustion of particulatematter accumulated in the detection part of the particulate mattersensor element. This eliminates the accumulated particulate matter fromthe detection part of the particulate matter sensor element. This canprevent incorrect detection of the particulate matter detection sensorcaused by the particulate matter remained in the detection part, andprevent the output of the particulate matter detection sensor from beingseparated from a correct output value. According to the presentinvention, it is possible for the particulate matter detection sensor tooutput a stable and correct detection signal with high accuracyregardless of operation conditions and environmental condition of theinternal combustion engine even if it is before or after the start orstop of the internal combustion engine.

In the control device as another aspect of the present invention, thecontrol part further comprises an electric power supply timing meanswhich determines a timing to supply electric power to the heater part,counted from a time when the internal combustion engine is started to atime when the electric power is supplied to the heater part on the basisof the operation state of the internal combustion engine.

In general, when the internal combustion engine is restarted, there is apossibility of adhering water contained in the inside of the exhaust gaspipe to the particulate matter sensor element of the particulate matterdetection sensor and causing incorrect detection of the particulatematter detection sensor. Further, there is a possibility for theparticulate matter detection sensor to be broken by adhering water tothe particulate matter detection sensor. In order to avoid this problem,the electric power supply timing means in the control device accordingto the present invention delays the time to supply electric power to theheater part of the particulate matter sensor element. It is thereforepossible to prevent the breaking of the particulate matter detectionsensor by adhering water. The control device according to the presentinvention allows the particulate matter detection sensor to output acorrect detection signal with high accuracy.

0014

In the control device as another aspect of the present invention, theelectric power supply timing means calculates an amount (or degree ofrisk) of condensed water remained in the exhaust gas pipe adhering tothe detection part in the particulate matter detection sensor, anddelays the timing to supply the electric power to the heater part on thebasis of the calculated amount of condensed water.

According to the present invention, the electric power supply timingmeans in the control device calculates the timing when the electricpower is supplied to the heater part on the basis of the calculatedamount (or the degree of risk) of condensed water adhering to thedetection part in the particulate matter detection sensor. This controlmakes it possible to avoid the problem caused by adhering watercontained in the exhaust gas pipe to the particulate matter detectionsensor.

In the control device as another aspect of the present invention, thecombustion control means supplies the electric power to the heater partin order to maintain the detection part of the particulate matterdetection sensor at the predetermined temperature T1 within a range ofnot less than 600° C. to not more than 900° C.

The combustion control means in the control device according to thepresent invention executes the combustion control executed when theinternal combustion engine is started so that the detection part in theparticulate matter sensor element is maintained at the temperature T1which is within the range of not less than 600° C. to not more than 900°C. This combustion control makes it possible to maintain the durabilityof the particulate matter sensor element and completely eliminateaccumulated particulate matter from the particulate matter sensorelement in the particulate matter detection sensor. Further, thiscombustion control can suppress energy cost.

In the control device as another aspect of the present invention, thecombustion control means supplies the electric power to the heater partin order to maintain the detection part of the particulate matterdetection sensor at the predetermined temperature T1 of not less than650° C. for the predetermined period S1 of time of not less than 20seconds.

The combustion control means in the control device according to thepresent invention executes the combustion control executed when theinternal combustion engine is started so that the detection part in theparticulate matter sensor element is maintained at the temperature T1 ofnot less than 650° C. for the period S1 of time of not less than 20seconds. This combustion control makes it possible to completelyeliminate accumulated particulate matter from the particulate mattersensor element with high efficiency.

In the control device as another aspect of the present invention, theusual control means supplies the electric power to the heater part inorder to maintain the detection part of the particulate matter detectionsensor at a predetermined temperature within a range of not less than50° C. to not more than 600° C.

The usual control means in the control device according to the presentinvention executes the usual control in order to maintain the detectionpart at a temperature within a range of not less than 50° C. to not morethan 600° C. The usual control makes it possible to allow a stableoutput, namely, a correct detection signal output from the particulatematter detection sensor.

In the control device as another aspect of the present invention, thedetection part is comprised of the pair of the detection electrodeshaving a comb shape and detection lead parts formed on a front surfaceof the insulation substrate. The heater part is comprised of heaterelectrodes and heater lead parts formed at the front end in a backsurface of the insulation substrate.

According to the present invention, it is possible to easily produce theparticulate matter sensor element in the particulate matter detectionsensor because the detection part is comprised of the pair of thedetection electrodes and detection lead parts formed on a front surfaceof the insulation substrate. On the other hand, the heater part iscomprised of heater electrodes and heater lead parts formed at the frontend in the back surface of the insulation substrate.

BRIEF DESCRIPTION OF THE DRAWINGS

A preferred, non-limiting embodiment of the present invention will bedescribed by way of example with reference to the accompanying drawings,in which:

FIG. 1A is a perspective view showing a schematic structure of aparticulate matter (PM) sensor element in a PM detection sensor and acontrol circuit according to an embodiment of the present invention;

FIG. 1B is a schematic view showing an entire configuration of anexhaust gas purifying system of a diesel engine for an motor vehicle towhich the PM detection sensor and the control circuit according to theembodiment of the present invention are applied;

FIG. 2 is an enlarged view showing a cross section of a part of the PMdetection sensor according to the embodiment of the present inventionwhich is mounted to an exhaust gas pipe in the exhaust gas purifyingsystem shown in FIG. 1B;

FIG. 3 is a flow chart showing the process for the control circuit tosupply electric power to a heater part in the PM sensor element in thePM detection sensor according to the embodiment of the presentinvention;

FIG. 4 is a flow chart showing a detailed process of a combustioncontrol executed when an internal combustion engine is started;

FIG. 5 is a view showing an experimental result of a relationshipbetween the temperature T1 (C) of the PM sensor element and the periodS1 (seconds) of time to maintain the temperature of the PM sensorelement in the PM detection sensor according to the embodiment of thepresent invention;

FIG. 6A is a timing chart showing the output change of the PM detectionsensor when the usual control is continuously executed;

FIG. 6B is a timing chart showing the output change of the PM detectionsensor when the diesel engine is restarted after the engine stop withoutexecuting the PM detection sensor regeneration control after thedetection process is executed by the PM detection sensor during theusual control; and

FIG. 6C is a timing chart showing the output change of the PM detectionsensor when the combustion control is executed at the engine start, buta PM detection sensor regeneration control is not executed before theengine stop.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Hereinafter, various embodiments of the present invention will bedescribed with reference to the accompanying drawings. In the followingdescription of the various embodiments, like reference characters ornumerals designate like or equivalent component parts throughout theseveral diagrams.

Embodiment

A description will be given of a particulate matter detection sensor 1and a control circuit 2 as a control device according to an embodimentof the present invention with reference to FIG. 1 to FIG. 6A, FIG. 6Band FIG. 6C.

The embodiment applies the particulate matter detection sensor 1(hereinafter, referred to the “PM detection sensor 1”) to an exhaust gaspurifying system of an internal combustion engine.

FIG. 1A is a perspective view showing a schematic structure of aparticulate matter sensor element 10 (hereinafter, referred to the “PMsensor element 10”) in the PM detection sensor 1 and the control device2 according to the embodiment of the present invention. FIG. 1B is aschematic view showing an entire configuration of the exhaust gaspurifying system of an on-vehicle diesel engine of an motor vehicle towhich the PM detection sensor 1 and the control device 2 according tothe embodiment of the present invention are applied. FIG. 2 is anenlarged view showing a cross section of a part of the PM detectionsensor 1 according to the embodiment of the present invention. Inparticular, the PM detection sensor 1 is mounted to an exhaust gas pipeEX in the exhaust gas purifying system of an on-vehicle diesel engine asan internal combustion engine shown in FIG. 1B.

The diesel engine E/G shown in FIG. 1B is equipped with a common railfuel injection system. The common rail fuel injection system increasesthe pressure of fuel by a high-pressure pump PMP. The common rail Rstores the fuel at a constant high pressure and supplies the highpressure fuel to each of the cylinders by an injector INJ.

The PM detection sensor 1 is placed at the downstream side of the dieselparticulate filter DPF in the exhaust gas pipe EX of the diesel engineE/G. The control circuit 2 as the control device and each of parts ofthe diesel engine E/G control the operation of the PM detection sensor1. The control circuit 2 and the control method will be explained indetail later.

A description will now be given of the structure of the exhaust gaspurifying system of the on-vehicle diesel engine of an motor vehiclewith reference to FIG. 1B.

As shown in FIG. 1B, a turbine TRB is mounted to an exhaust gas manifoldof the diesel engine E/G. When a turbo charger TRB_(CGR) in accordancewith the rotation of the turbine TRB, compressed air is supplied to theintake manifold MH_(IN) through an intercooler CLR_(INT).

A part of the exhaust gas discharged from an outlet manifold MH_(EX) isre-circulated to the intake manifold MH_(IN) through an EGR valveV_(EGR) and an EGR cooler CLR_(EGR). Forced induction increases thequantity of intake air in order to increase combustion efficiency andEGR (Exhaust Gas Recirculation) suppresses the combustion of the dieselengine in order to suppress nitrogen oxide (NOx) from being dischargedto the ambient atmosphere of the motor vehicle.

A unit having diesel oxidation catalyst DOC and a diesel particulatefilter DPF are mounted to the exhaust gas pipe EX connected to theoutlet manifold MH_(EX) in order to purify the exhaust gas emitted fromthe diesel engine. That is, un-burned components such as hydro carbonHC, carbon monoxide and nitric oxide NO are oxidized when the exhaustgas passes through the exhaust gas pipe EX after emitted from the dieselengine, and the diesel particulate filter DPF traps soot (Soot), solubleorganic fraction (SOF) and particulate matter (PM) composed of inorganiccomponents contained in the exhaust gas. The diesel particulate filterDPF is placed at the downstream side of the unit having the dieseloxidation catalyst (DOC), as shown in FIG. 1B.

In general, such a diesel oxidation catalyst DOC is supported on asurface of a known monolith support, for example, a ceramic honeycombstructure body made of cordierite. When the diesel particulate filterDPF is forcedly regenerated, fuel is supplied and burned in oxidation.This increases the temperature of the exhaust gas and the dieseloxidation catalyst DOC oxides and eliminates soot of fraction (SOF)components contains in particulate matter PM. Nitrogen dioxide NO₂generated by oxidizing nitric oxide NO is used as oxidizing agent ofparticulate matter PM accumulated in the DPF which is placed at thedownstream side of the unit having the diesel oxidation catalyst DOC.This makes it possible to execute continuous oxidizing.

The diesel particulate filter DPF has a filter structure of a wall flowtype which is well known. For example, a porous ceramic honeycombstructure body is extruded and molded. The porous ceramic honeycombstructure body is made of heat resistance ceramics such as cordierite.On the inlet surface of the diesel particulate filter DPF, cells arealternately plugged by plug members so that the surface of the inletsurface has a checkered pattern in which one of adjacent cells isplugged and the other cell is open, and the outlet surface has thecheckered pattern in which one of adjacent cells is plugged and theother cell is open. That is, the diesel particulate filter DPF iscomposed of a plurality of cells formed by cell walls. One end part ofeach of the cells is open and the other end part thereof is plugged sothat the plugged parts are alternately formed on each of the inletsurface and the outlet surface of the diesel particulate filter DPF.

Each of the cells is formed in parallel along the longitudinal directionof the diesel particulate filter DPF. In particular, the cell walls inthe adjacent cells have porous structure through which the exhaust gaspasses. The porous structure of the cell walls (porous cell walls) trapsparticulate matter PM contained in the exhaust gas when the exhaust gaspasses through the porous cell walls.

It is possible to form a continuous type diesel particulate filtercomposed of the diesel oxidation catalyst DOC and the diesel particulatefilter DPF.

A differential pressure sensor SP is placed in the exhaust gas pipe EXin order to monitor the quantity of particulate matter PM accumulated inthe diesel particulate filter DPF.

The differential pressure sensor SP is connected to the exhaust gas pipeEX at the upstream side and the downstream side of the dieselparticulate filter DPF through pressure introduction pipes. Thedifferential pressure sensor SP detects the pressure of the exhaust gasat the upstream side and the downstream side of the diesel particulatefilter DPF, respectively, and outputs a detection signal correspondingto the pressure difference detected at the upstream side and thedownstream side of the diesel particulate filter DPF.

Further, temperature sensors S1, S2 and S3 are placed at the upstreamside of the unit having the diesel oxidation catalyst DOC, the upstreamside and the downstream side of the diesel particulate filter DPF inorder to detect the temperature of the exhaust gas.

The control circuit 2 receives the detection signals transferred fromthese sensors and monitors the activation state of the diesel oxidationcatalyst DOC and the quantity of particulate matter PM accumulated inthe diesel particulate filter DPF on the basis of the detection signals.When the quantity of particulate matter PM accumulated in the dieselparticulate filter DPF exceeds a predetermined allowable value, thecontrol circuit 2 forcedly executes the process of burning theparticulate matter PM accumulated in the diesel particulate filter DPFin order to regenerate the diesel particulate filter DPF and eliminatethe particulate matter PM from the diesel particulate filter DPF.

Further, the particulate matter detection sensor (PM detection sensor) 1detects particulate matter PM which passes through the dieselparticulate filter DPF and travels to the downstream side of the dieselparticulate filter DPF.

As shown in FIG. 1A, the PM detection sensor 1 is composed of aparticulate matter sensor element (PM sensor element) 10. The PM sensorelement 10 is composed of an insulation substrate 13, a pair ofdetection electrodes 11 and 12, a pair of electrode leads 111 and 121,and a heater part 300. The insulation substrate 13 is made of electricalinsulation material. The pair of the detection electrodes 11 and 12 andthe pair of the electrode leads 111 and 121 are formed on one surface ofthe insulation substrate 13. The detection electrodes 11 and 12 make thedetection part 100. The heater part 300 is formed or laminated on theother surface of the insulation substrate 13. The heater part 300generates heat energy in order to heat the detection part 100 whenreceiving electric power.

The detection part 100 is connected to the control circuit 2 through theelectrode leads 111 and 121. The detection part 100 detects a resistancevalue between the detection electrodes 11 and 12 and outputs a detectionsignal corresponding to the detected resistance value. The heater part300 is composed of a heater electrode 31 and heater leads 311 and 321.The heater electrode 31 and the heater leads 311 and 321 are formed onthe surface of the insulation substrate 32. The heater part 300 isconnected to the heater power source 21 through the heater leads 311 and321. The control circuit 2 instructs the heater power source 21 tosupply electric power to the heater part 300.

The detection part 100 is produced by the following method. For example,ceramic material having alumina of a superior electric insulation and asuperior heat resistance is formed on the insulation substrate 13 of aplate shape by using doctor blade, and press mold method. The detectionelectrodes 11 and 12 are formed at the front end of the insulationsubstrate 13 so that the detection electrodes 11 and 12 have a combstructure in which the detection electrodes 11 and 12 alternately faceto each other at a predetermined gap. The detection electrodes 11 and 12are formed by printing conductive paste containing noble metal such asplatinum Pt in a predetermined pattern on a surface (or a front surface)of the insulation substrate 13. The detection electrodes 11 and 12 areconnected to one end terminal of each of the electrode leads 111 and 121formed on the surface of the insulation substrate 13.

On the other hand, the heater part 300 is produced by printing theheater electrodes 30 and the heater leads 311 and 312 in a predeterminedpattern on the surface (the detection part 100 side) of the insulationsubstrate 32 by using the same method. The heater electrodes 31 of theheater part 300 are formed directly below the detection electrodes 11and 12 in order to heat the detection part 100 at a predeterminedtemperature with good efficiency. In other words, the detectionelectrodes 11 and 12 are formed on the front surface of the entireinsulation substrate composed of the insulation substrate 12 and theinsulation substrate 32. The insulation substrate 12 and the insulationsubstrate 32 are stacked. The heater part 300 is formed on the backsurface of the entire insulation substrate composed of the insulationsubstrate 12 and the insulation substrate 32.

As shown in FIG. 2, the PM detection sensor 1 has a cylindrical housingcase 50 which is screwed into the wall of the exhaust gas pipe EX. ThePM detection sensor 1 accommodates the upper half of the PM sensorelement 10 which is inserted into and fixed to a cylindrical insulator60. The bottom half of the PM sensor element 10 is fixed to the basepart of the cylindrical housing case 50 and placed in a hollow coverbody 40. The hollow cover body 40 with the bottom half of the PM sensorelement 10 projects in the inside of the exhaust gas pipe EX. inletholes 410 and 411 are formed in the base part and the side part of thehollow cover body 40 in order to introduce the exhaust gas in theexhaust gas pipe EX. The exhaust gas flows from the diesel particulatefilter DPF and contains particulate matter PM.

In order to trap particulate matter PM contained in the exhaust gas, asshown in FIG. 2, it is preferable to place the PM detection sensor 1 inthe exhaust gas pipe EX so that the detection part 100 in the PM sensorelement 10 faces the upstream side of the exhaust gas pipe EX. Further,it is possible to avoid incorrect detection caused by accumulatingparticulate matter PM between the electrode leads 111 and 121 when thePM sensor element 10 has a structure in which an insulation protectionlayer 14 is formed on the surface of the insulation substrate 13excepting the detection part 100 so that the electrode leads 111 and 121are covered with the insulation protection layer 14.

Next, a description will now be given of the basic operation of the PMdetection sensor 1 according to the present invention.

As shown in FIG. 2, the exhaust gas of the diesel engine E/G isintroduced into the inside of the PM detection sensor 1 through theintake hole 411 which is formed in the cover body 40 of the PM detectionsensor 1. The intake hole 411 faces to the upper stream side of theexhaust gas in the exhaust gas pipe EX. After being in contact with thePM sensor element 10, the exhaust gas is discharged into the exhaust gaspipe EX as the outside of the PM detection sensor 1 through the hole 410formed in the base surface or the hole 411 faced to the downstream sideof the exhaust gas.

As shown in FIG. 1A, the detection electrodes 11 and 12 having a combstructure at a predetermined gap formed on the surface of the detectionpart 100. When the PM detection sensor 1 is in its initial condition, nocurrent flows between the detection electrodes 11 and 12 because noparticulate matter PM is accumulated between the detection electrodes 11and 12. When the exhaust gas is introduced into the PM detection sensor1, particulate matter PM of conductive characteristics is graduallyaccumulated between the detection electrodes 11 and 12. When thequantity of particulate matter PM accumulated between the detectionelectrodes 11 and 12 exceeds a predetermined value, a current flowsbetween the detection electrodes 11 and 12. The more the quantity ofparticulate matter PM is increased, the more the resistance valuebetween the detection electrodes 11 and 12 is decreased. It is thereforepossible to detect the resistance value between the detection electrodes11 and 12 on the basis of this phenomenon. That is, it is possible toexecute the diagnosis of detecting defect or failure of the dieselparticulate filter DPF on the above relationship.

For example, when a defect such as cell-wall defect occurs in the dieselparticulate filter DPF, the diesel particulate filter DPF cannot executea correct operation of trapping particulate matter PM contained in theexhaust gas. This increases the quantity of particulate matter PMcontained in the exhaust gas discharged from the diesel particulatefilter DPF.

The control circuit 2 monitors the quantity of particulate matter PMpassing through the diesel particulate filter DPF during a predeterminedperiod of time by using the PM detection sensor 1. When the monitoredquantity of particulate matter PM is clearly larger than usual quantity,the control circuit 2 judges an occurrence of failure in the dieselparticulate filter DPF. Even if the diesel particulate filter DPF is inthe usual condition, when the quantity of particulate matter PMaccumulated between the detection electrodes 11 and 12 in the PM sensorelement 10 exceeds the predetermined value, the change rate of theresistance value between the detection electrodes 11 and 12 becomes low,that is, the detection accuracy of the PM detection sensor 1 isdecreased. In order to avoid this drawback, it is preferable to executethe regeneration of the PM detection sensor 1 at a predetermined periodof time.

By the way, if the diesel engine E/G is stopped and restarted withoutexecuting the regeneration of the PM detection sensor 1, particulatematter PM previously adhered to the detection electrodes 11 and 12 inthe PM detection sensor 1 is remained. In this case, the characteristicsof particulate matter PM are changed according to the environmentalcondition when the diesel engine E/G is stopped and restarted. Thisinfluences the output of the PM detection sensor 1. For example, whenthe diesel engine E/G is stopped under the high temperature of theexhaust gas pipe EX, there is a possibility of evaporating solubleorganic fraction (SOF) only contained in the particulate matter PMbetween the detection electrodes. This changes the conductivity ofparticulate matter PM, the output of the PM detection sensor 1 is alsochanged when the diesel engine E/G is restarted. Further, when thediesel engine E/G is started in cold environment, there is a possibilityof adhering water or dew condensation onto the detection part of thedetection electrodes 11 and 12. This changes the conductivity ofparticulate matter PM, the output of the PM detection sensor 1 is alsochanged when the diesel engine E/G is restarted. This causes incorrectoutput of the PM detection sensor 1 because the accumulation ofparticulate matter PM between the detection electrodes 11 and 12 ischanged or the water is evaporated. The above conditions when the dieselengine E/G is started are different every time. Because soluble organicfraction (SOF) is not evaporated, but hardened or burnt according to thechange of the temperature and conditions (for example, concentration ofoxygen) of the exhaust gas, it is difficult to predict the magnitude ofincorrect output of the PM detection sensor 1.

In order to solve the above problems causing incorrect output of the PMdetection sensor 1, the control circuit 2 adjusts the supply of electricpower to the heater part 300 at the engine start and the execution ofthe usual control. That is, the control circuit 2 firstly executes theprocess of burning and eliminating particulate matter PM accumulated (orremained) in the PM detection sensor 1 when the diesel engine E/G isstarted. The control circuit 2 then executes the usual control processwhich detects the presence and quantity of particulate matter containedin the exhaust gas. Thereby, the control circuit 2 suppresses thefluctuation of the output of the PM detection sensor 1 and avoidscausing incorrect detection of the PM detection sensor 1 by burning theaccumulated particulate matter PM and eliminating the accumulatedparticulate matter PM from the PM detection sensor 1 when the dieselengine E/G is started.

Specifically, the control circuit 2 instructs the heater power source 21to supply electric power to the heater part 300 when the diesel engineE/G is started. The detection part 100 of the PM detection sensor 1 isthereby heated at the temperature T1 during the period S1 of time. Thetemperature T1 allows the detection part 100 to burn and eliminate theaccumulated particulate matter PM. That is, the control circuit 2executes the combustion control at the engine start. In the combustioncontrol executed at the engine start particulate matter PM accumulatedon the surface of the detection part 100 is burned and eliminatedcompletely. This combustion control at the engine start corresponds tothe function executed by the combustion control means used in theclaims.

After the combustion control at the engine start, the control circuit 2adjusts the electric power supply to the detection part 100 in order tomaintain the detection part 300 at a temperature T2 which is within atemperature range of less than the temperature T1. This control allowsthe PM detection sensor 1 to detect particulate matter PM adhered on thedetection electrodes 11 and 12 (as the usual control means used in theclaims).

In the combustion control at the engine start, when the diesel enginestart and the electric power supply to the heater part 300 aresimultaneously executed, condensed water is scattered in the exhaust gaspipe EX, and the scattered water is adhered to the detection part 100 inthe PM detection sensor 1 of a high temperature. When the scatteredwater is adhered to the PM detection sensor 1 of a high temperature, thePM detection sensor 1 is broken. In order to avoid this, it is necessaryto delay the time to start the electric power supply to the PM sensorelement 10 until the condensed water in the exhaust gas pipe EX is driedor no condensed water is adhered to the PM sensor element 10.

In order to ensure the above problem, it is necessary for the controlcircuit 2 to calculates an amount (or degree of risk) of condensed waterremained in the exhaust gas pipe adhering to the detection part 100 inthe particulate matter detection sensor 1 on the basis of the operationcondition of the diesel engine E/G, and to delay the execution of theelectric power supply to the heater part 300 on the basis of thecalculated amount (or degree of risk) of condensed water. That is, it ispreferable for the control circuit 2 to delay the execution of theelectric power supply to the heater part 300 until the amount (or degreeof risk) of condensed water adhering to the detection part 100 in the PMdetection sensor 1 is entered into its allowable range. It is alsopossible to use the relationship between the timing when the electricpower supply to the detection part 100 and a coefficient correspondingto the calculated amount (or degree of risk) of condensed water adheringto the detection part 100 which is calculated on the basis of theoperation condition of the diesel engine E/G. In the latter case, thecontrol circuit 2 starts the electric power supply to the detection part100 in the PM sensor element 10 at the timing which is determined on thebasis of the coefficient corresponding to the amount (or degree of risk)of condensed water adhering to the detection part 100. This controlmakes it possible to detect the quantity of particulate matter PMadhered to the PM detection sensor 1 with high accuracy whilesuppressing the detection part 100 from being broken by adheringcondensed water to the detection part 100.

A description will be given of the control operation of the controlcircuit 2 with reference to FIG. 3 and FIG. 4.

FIG. 3 is a flow chart showing the process for the control circuit 2 tosupply electric power to the heater part 100 in the PM detection sensor1 according to the embodiment of the present invention.

As shown in FIG. 3, when the diesel engine E/G is started, the controlcircuit 2 receives detection signals transferred from various sensors(step S100). At this time, in order to detect the operation condition ofthe diesel engine E/G and the temperature condition in the exhaust gaspipe EX, the control circuit 2 receives detection signals transferredfrom a water temperature sensor (not shown) and an oil temperaturesensor (not shown). The water temperature sensor detects the temperatureof engine cooling water. The oil temperature sensor detects thetemperature of lubricating oil.

The control circuit 2 further receives a detection signal transferredfrom an intake air temperature sensor. The intake air temperature sensoris embedded in an air flow meter AFM capable of detecting thetemperature of ambient air. Still further, the control circuit 2receives a detection signal transferred from a temperature sensor S3which is placed at the downstream side of the diesel particulate filterDPF in order to detect the temperature of the exhaust gas around the PMdetection sensor 1. Still further, the control circuit 2 receives thedetection signal transferred from the rotation sensor capable ofdetecting the rotation of the diesel engine E/G, the detection signaltransferred from a sensor capable of detecting the quantity of fuelinjection, and the detection signal transferred from a sensor capable ofdetecting the operation time length of the diesel engine E/G.

In step S101, the control circuit 2 calculates an amount (or degree ofrisk) of condensed water adhering to the detection part 100 in the PMsensor element 10 in the PM detection sensor 1 on the basis of theinformation obtained from the received detection signals transferredfrom the various sensors. Specifically, the control circuit 2 predictsthe quantity of condensed water which is generated and stayed in theinside of the exhaust gas pipe EX at the upstream of the PM detectionsensor 1 on the basis of the elapsed period of time, the operationcondition and temperature condition of the diesel engine E/G after theengine start, where, the elapsed period of time is the time lengthcounted form the time when the diesel engine E/G is previously startedto the current time.

The control circuit 2 then calculates the amount (or degree of risk) ofcondensed water adhering to the detection part 100 in the PM detectionsensor 1 by using the relationship obtained in advance on the basis ofthe shape of the exhaust gas pipe EX. For example, the ambienttemperature is low, water is condensed in the exhaust gas pipe EX whenthe temperature of the exhaust gas pipe EX is decreased after the enginestop or when exhaust gas is introduced into the inside of the exhaustgas pipe EX at a low temperature immediately after the engine start.Further, when the temperature of the exhaust gas pipe EX is relativelyhigh in a short elapsed period of time after the engine stop, thequantity of condensed water is low, and the condensed water can beevaporated within a short period of time. Still further, even if havingthe same quantity of condensed water, it is possible to easily generatecondensed water in the exhaust gas pipe EX when the exhaust gas pipe EXhas a curved shape. It is often difficult to scatter the condensed waterin the exhaust gas pipe EX having such a curved shape. Accordingly, itis necessary to make an additional map in advance on the basis ofexperimental results obtained by considering the above conditions. It isalso possible to calculate the amount (or degree of risk) of condensedwater adhering to the detection part 100 in the PM detection sensor 1 byusing the equation which considers the above conditions.

In step S102, the control circuit 2 detects whether or not thecalculated amount (or degree of risk) of condensed water, whichindicates a probability that condensed water is sc adhered to the PMdetection sensor 1, is less than a predetermined value. Thepredetermined value is the minimum value of causing the PM sensorelement 10 in the PM detection sensor 1 breaking when the electric poweris supplied to the PM detection sensor 1. When the detection result instep S102 indicates affirmative (“YES” in step S102), there is nopossibility of breaking the PM detection sensor 1. The operation flowgoes to step S103. In step S103, the control circuit 2 executes thecombustion control in order to start the operation of the diesel engineE/G.

On the other hand, when the detection result in step S102 indicatesnegative (“NO” in step S102), there is a possibility of breaking the PMdetection sensor 1. The operation flow is returned to step S100. Thecontrol circuit 2 continues the routine of steps S100, S101 and S102until there is no more possibility of breaking the PM sensor 1 in orderto delay the start of supplying electric power to the heater part 300.

In step S103, the control circuit 2 executes the combustion control atthe engine start. Specifically, the control circuit 2 instructs theheater power source 21 to supply electric power to the heater part 300in the PM detection sensor 1 in order to burn and eliminate particulatematter PM accumulated in the detection part 100.

A description will now be given of the combustion control which isexecuted when the diesel engine E/G is started or restarted withreference to FIG. 4.

FIG. 4 is a flow chart showing a detailed process of the combustioncontrol at the engine start.

In step S200, the control circuit 2 receives various data items in orderto obtain the information regarding the quantity of particulate matterPM accumulated in the detection part 100 in the PM sensor element 10 inthe PM detection sensor 1. The information is:

(a1) Period of time counted from the time when the PM combustion wasexecuted in the previous usual control to the time when the dieselengine E/G was stopped;

(a2) Period of time counted from the time when diesel engine E/G waslast stopped to the current time; and

(a3) Period of time counted from the time at the current engine start tothe time when the combustion control at the engine start is started.

The control circuit 2 receives the operation state of the diesel engineE/G and the temperature and time conditions of the operation of thediesel engine E/G, for example, receives the following data items inorder to detect the quantity of particulate matter PM adhered to andaccumulated in the detection part 100 in the PM sensor element 10 of thePM detection sensor 1 and the change of the quantity of particulatematter PM in each of the periods (a1), (a2) and (a3):

(b1) Temperature of cooling water of the diesel engine E/G;

(b2) Temperature of lubricating oil;

(b3) Temperature of ambient atmosphere;

(b4) Temperature of exhaust gas;

(b5) Rotation number or speed of the diesel engine E/G; and

(b6) Quantity Q of injection fuel.

In step S201, the control circuit 2 detects and calculates followingvalues:

(c1) Quantity of particulate matter PM accumulated in the detection part100 in the PM sensor element 10 of the PM detection sensor 1 at theprevious engine stop;

(c2) Quantity of water and hydro carbon (HC) which are adhered to the PMdetection sensor 1 or evaporated in the exhaust gas pipe EX during theengine stop; and

(c3) Quantity of particulate matter PM to be adhered and accumulated inthe detection part 100 in the PM sensor element 10 of the PM detectionsensor 1 during the period of time counted from the current engine startto the time when the combustion control at the engine start is started.

Because the change of each of the quantity of accumulated particulatematter PM during the operation of the diesel engine E/G, the quantity ofwater and hydro carbon (HC) during the engine stop is fluctuated by theoperation state of the diesel engine E/G and the environment of theinside of the exhaust gas pipe EX. Accordingly, the control circuit 2calculates these changes by using the experimental map which is obtainedin advance or a theoretical arithmetic equation.

The operation flow goes to step S202. In step S202, the control circuit2 calculates the combustion condition (Temperature and Period of time)of burning particulate matter PM accumulated in the detection part 100in the PM sensor element 10 of the PM detection sensor 1 on the basis ofthe adhesion condition (quantity and composition of particulate matterPM) of particulate matter PM calculated in step S201.

In general, it is preferable to burn accumulated particulate matter PMat the temperature T1 during the combustion control at the engine start.This temperature T1 is not less than the allowable temperature at whichparticulate matter PM can be completely burned. In the view of heatresistance of the heater part 300 in the PM sensor element 10, it ispreferable for the temperature T1 to be not more than 900° C.

Because the period S1 of time depends on the temperature T1, the morethe temperature T1 is increased, the more the period S1 of time isdecreased. It is preferable for the period S1 of time to be not morethan 5 minutes.

FIG. 5 is a view showing an experimental result of a relationshipbetween the temperature of the PM sensor element 10 and the period oftime to maintain the temperature of the PM sensor element 10 in the PMdetection sensor 1 according to the embodiment of the present invention.

The experimental condition with which the experimental result shown inFIG. 5 is obtained is as follows.

As shown in FIG. 1B and previously described, the PM detection sensor 1is mounted to the exhaust gas pipe EX. The control circuit 2 instructedthe heater power source 21 to supply electric power to the heater part300 in the Pm sensor element 10 of the PM detection sensor 1 after theengine start in order to maintain the PM sensor 1 at the predeterminedtemperature T1 for the predetermined period S1 of time. The quantity ofparticulate matter PM accumulated in the PM sensor element 10 of the PMdetection sensor 1 was detected. During this detection, the PM sensorelement 10 was maintained at the temperature within a range of 550° C.to 750° C., and the period S1 of time was changed.

As shown in FIG. 5, it is possible to eliminate the particulate matterPM from the detection part 100 of the PM sensor element 10 of the PMdetection sensor 1 when the predetermined temperature T1 was 600° C. andthe period S2 of time was not less than 20 minutes, and when thepredetermined temperature T1 was 700° C. and the period S2 of time wasnot less than 10 minutes.

However, it is difficult to completely eliminate the accumulatedparticulate matter PM from the detection part 100 of the PM sensorelement 10 when the predetermined temperature T1 was not more than 550°C. and the period S2 of time was 80 minutes. The above experimentalresults shown in FIG. 5 indicates that it is necessary to maintain thePM detection sensor 1 at the temperature T1 of not less than 600° C.,preferably, at the temperature T1 of not less than 650° C. for theperiod S1 of time of not less than 20 seconds.

In step S203, the control circuit 2 executes the combustion control atthe engine start in order to burn the accumulated particulate matter PMand eliminate them from the PM sensor element 10. That is, in step S203,the control circuit 2 instructs the heater power source 21 to supplyelectric power to the heater part 300 of the PM sensor element 10 in thePM detection sensor 1 under the conditions (temperature T1 and period S1of time) which are determined in step S202. This control makes itpossible to heat the detection part 10 at the temperature T1 for theperiod S2 of time. The operation flow goes to step S2104. In step S204,the control circuit 2 completes the combustion control at the enginestart.

Return to the flow chart shown in FIG. 3, the operation flow progressesto step S104. In step S104, the control circuit 2 executes the usualcontrol. In the usual control in step S104, the electric power issupplied to the heater part 300 of the PM sensor element 10 of the PMsensor 1 in order to maintain the detection part 100 at the temperatureT2 which is lower than the temperature T1. The execution of the usualcontrol makes it possible to detect the quantity of particulate matterPM accumulated in the detection part 100 of the PM sensor element 10. Aspreviously described, the temperature T1 is used during the combustioncontrol executed when the engine is started (or restarted).Specifically, during the usual control after completion of thecombustion control executed during the engine start, the control circuit2 maintains the detection part 100 in the PM sensor element 10 at thetemperature T2 within a range of 50° C. to 600° C. This control makes itpossible for the PM detection sensor 1 to output a stable detectionsignal.

FIG. 6A is a timing chart showing the output change of the PM detectionsensor 1 when the usual control is continuously executed. FIG. 6A showsthe characteristics of the output of the PM detection sensor. The outputof the PM detection sensor is increased when the pair of the detectionelectrodes in the detection part is conducted after a period of timecounted from the PM sensor detection is executed, and the output of thePM detection sensor is rapidly increased according to the elapsed oftime and saturated.

This means that the resistance value between the detection electrodes isdecreased according to increasing the quantity of particulate matter PMaccumulated in the detection part of the PM sensor element. When thequantity of particulate matter PM accumulated in the detection partexceeds a predetermined value, the resistance value between them is notchanged. Accordingly, it is necessary to execute the sensor regenerationcontrol periodically in order to eliminate the particulate matter PMfrom the detection part of the PM sensor element of the PM detectionsensor. The sensor regeneration control in this case can be executed inparallel to the execution of the combustion control at the engine start.That is, it is sufficient to maintain the PM sensor at the predeterminedtemperature for the predetermined period of time which allows theaccumulated particulate matter from being burned. For example, it ispreferable to maintain the PM sensor at a temperature within a range of600° C. to 900° C. for not less than 20 seconds, in more preferable, ata temperature within a range of 650° C. for not less than 20 seconds, ormaintain it at the temperature of 700° C. for 10 seconds. After this,the same steps are continuously executed, as previously described.

FIG. 6B is a timing chart showing the output change of the PM detectionsensor when the diesel engine is restarted (without executing thecombustion control at the engine start according to the embodiment ofthe present invention) after the engine stop without executing the PMdetection sensor regeneration control after the detection process isexecuted by the PM detection sensor during the usual control.

The left side in FIG. 6B shows the case when the diesel engine E/G isstopped after the detection electrodes and in the pair in the detectionpart of the PM sensor element are electrically conducted and the PMdetection sensor starts to output the detection signal. In this case,the combustion control at the engine start is not executed when thediesel engine E/G is started (or restarted). At this time, thesensitivity of the PM detection sensor is changed when compared with thenormal output curve (designated by dotted line in FIG. 6B), and this hasa high possibility of executing incorrect detection of detecting thequantity of particulate matter PM accumulated in the detection partbecause the characteristics of accumulated particulate matter PM ischanged and water is adhered to the detection part when the dieselengine E/G is stopped (at engine stop soaking).

The right side in FIG. 6B shows the case in which the diesel engine E/Gis stopped during no output of the PM detection sensor after thedetection electrodes in the pair in the detection part of the PM sensorelement are electrically conducted and the PM detection sensor starts tooutput the detection signal. In this case shown in the right side inFIG. 6B, there is a high possibility of executing incorrect detection ofthe quantity of particulate matter PM accumulated in the detection partbecause particulate matter PM is accumulated between the detectionelectrodes after the PM detection sensor regeneration control is stillremained in the detection part of the PM sensor element. It is difficultto detect the quantity of particulate matter accumulated in thedetection part of the PM sensor element of the PM detection sensor withhigh accuracy.

FIG. 6C is a timing chart showing the output change of the PM detectionsensor 1 when the control circuit 2 executes the combustion control atthe engine start. That is, the combustion control is executed when thediesel engine E/G is started (or restarted). In the case shown in FIG.6C, the control circuit 2 does not execute the control of regeneratingthe PM detection sensor 1 before the diesel engine E/G is stopped.

FIG. 6C shows the case in which the control circuit 2 executes thecombustion control when the diesel engine E/G is started withoutexecuting the regeneration control of regenerating the PM detectionsensor before the engine stop. As shown in FIG. 6C, it is possible forthe present invention to execute the correct detection of detecting thequantity of particulate matter PM accumulated in the detection part 100between the detection electrodes 11 and 12 with high accuracy withoutcausing the fluctuation of the detection sensitivity of the PM detectionsensor and the change of the period of time in which the PM detectionsensor outputs no detection signal.

INDUSTRIAL APPLICABILITY

It is possible to place the PM detection sensor 1 according to thepresent invention at the downstream side of the diesel particulatefilter DPF and detect the failure of the diesel particulate filter DPFunder the control of the control circuit 2 according to the presentinvention. It is also possible to place the PM detection sensor 1according to the present invention at the upstream side of the dieselparticulate filter DPF and directly detect particulate matter PM whichis introduced into the diesel particulate filter DPF under the controlof the control circuit 2 according to the present invention.

While specific embodiments of the present invention have been describedin detail, it will be appreciated by those skilled in the art thatvarious modifications and alternatives to those details could bedeveloped in light of the overall teachings of the disclosure.Accordingly, the particular arrangements disclosed are meant to beillustrative only and not limited to the scope of the present inventionwhich is to be given the full breadth of the following claims and allequivalents thereof.

1. A control device of controlling a particulate matter detection sensorplaced in an exhaust gas pipe of an internal combustion engine throughwhich exhaust gas emitted from the internal combustion engine flows anddischarged to the outside, the particulate matter detection sensorhaving a particulate matter sensor element comprised of an insulationsubstrate, a detection part composed of a pair of detection electrodesformed on a surface of the insulation substrate, and a heater part ofgenerating heat energy when receiving electric power in order to heatthe detection part at a predetermined temperature, the control devicecomprising a control part which detects an electrical resistance valuebetween the pair of the detection electrodes in the detection part, theelectrical resistance value between the pair of the detection electrodesin the detection part changing in accordance with a change of quantityof particulate matter accumulated in the detection part, and the controlpart adjusting electric power supply to the heater part, the controlpart comprising: combustion control means which executes combustioncontrol when the internal combustion engine is started to operate, andin the combustion control, the combustion control means supplieselectric power to the heater part in order to maintain the detectionpart of the particulate matter detection sensor at a predeterminedtemperature T1 for a predetermined period S1 of time in order to burnthe accumulated particulate matter in order to eliminate the accumulatedparticulate matter from the detection part of the particulate matterdetection sensor; and usual control means which executes usual controlafter completion of the combustion control which is executed when theinternal combustion engine is started to operate, wherein in the usualcontrol, the usual control means supplies electric power to the heaterpart in order to maintain the detection part of the particulate mattersensor element at a temperature T2 which is less than the predeterminedtemperature T1 in order to detect particulate matter accumulated in thedetection part.
 2. The control device according to claim 1, wherein thecontrol part further comprises electric power supply timing means whichdetermines a time to supply electric power to the heater part, countedfrom a time when the internal combustion engine is started to a timewhen the electric power is supplied to the heater part on the basis ofthe operation state of the internal combustion engine.
 3. The controldevice according to claim 2, wherein the electric power supply timingmeans calculates an amount of condensed water remained in the exhaustgas pipe adhering to the detection part in the particulate matterdetection sensor, and delays the timing to supply the electric power tothe heater part on the basis of the calculated amount of condensedwater.
 4. The control device according to claim 1, wherein thecombustion control means supplies the electric power to the heater partin order to maintain the detection part of the particulate matterdetection sensor at the predetermined temperature T1 within a range ofnot less than 600° C. to not more than 900° C.
 5. The control deviceaccording to claim 4, wherein the combustion control means supplies theelectric power to the heater part in order to maintain the detectionpart of the particulate matter detection sensor at the predeterminedtemperature T1 of not less than 650° C. for the predetermined period S1of time of not less than 20 seconds.
 6. The control device according toclaim 1, wherein the usual control means supplies the electric power tothe heater part in order to maintain the detection part of theparticulate matter detection sensor at a predetermined temperaturewithin a range of not less than 50° C. to not more than 600° C.
 7. Thecontrol device according to claim 1, wherein the detection part iscomprised of the pair of the detection electrodes having a comb shapeand detection lead parts formed on a front surface of the insulationsubstrate, and the heater part is comprised of heater electrodes andheater lead parts formed at the front end in a back surface of theinsulation substrate.